Food products and other commodities are marketed in flexible sheet material from film made of air and moisture impervious plastic, the packages being formed either from precut sections of the flexible material or from a continuous length thereof. Some of the products so marketed are adversely affected by their exposure to air for a length of time, but they retain their desired characteristics if maintained in a package from which the air has been evacuated and flushed with an inert gas to insure the removal of all air.
Various machines or procedures have been utilized to evacuate the packages of the character described after inserting into the packages the food products or other commodities. In one type of machine, the packages containing the products are fed to a vacuum chamber, the chamber is sealed and the air is evacuated from the chamber. Upon arriving at the desired vacuum, the package which has been subjected to the vacuum within the chamber is sealed off by heat sealing means. With such machines a slit must be formed in the package before the package is fed to the vacuum chamber and while in the chamber a probe must be inserted through the slit to separate the upper and lower portions of the flexible package so that air can be evacuated and gas can be introduced. One drawback to this method of forming an evacuated package is that the upper and lower film webs are separated only in the vicinity of the probe leaving air trapped in the portions of the package which are remote from the slit. Accordingly, it is one object of the present invention to produce a gas flushed package without the necessity for using a probe.
Another drawback in prior art packages is that the evacuation of air and introduction of gas is done through a single opening or orifice so that there is not a complete sweep of the package by the removal of air and introduction of gas. Accordingly, it is another object of the present invention to evacuate a package from one side thereof and introduce gas from the other side thereby completely sweeping the package of residual air.
To be commercially attractive, the packaging machines and methods must be able to attain a sustained rate of production that makes the method economically feasible. However, when higher production speeds are attempted or attained it is often at the expense of package quality so that residual air remains within the package and the sealing of the package is distorted and wrinkled thereby being both unattractive and not securely sealed. Accordingly, there is still another object of the present invention to attain high vacuum levels within a package and distortion-free seals at commercially acceptable production rates.
These and other objects are achieved by the present invention which is described in the summary of invention below.